Polyolefin reaction products and derivatives thereof have long been used in the lubricant, fuels, metal working and other industries. Principle reaction products made from polyolefins are polyolefin substituted succinic anhydrides and dispersants made therefrom for use in lubricants and fuels. The literature abounds with examples of various routes used to make these reaction products which are in large part characterized by the halogen promoted reaction of polyolefins such as polyisobutylenes with .alpha.-.beta.unsaturated acids or anhydrides such as maleic anhydride to form polyolefin substituted succinic anhydrides. The anhydrides are further reacted with metal salts or with amines having one &gt;NH group or alcohols to form dispersants.
Problems with the current situation for the synthesis of lubricant additives outlined above is that they have a high halogen content which is causing increased environmental concerns for the continued use of the lubricants and fuels containing them.
A heretofore preferred manner of making lubricant additives has been to alkylate .alpha.-.beta. unsaturated acids or anhydrides in the presence of chlorine. This type of reaction yields halogen containing polyalkenyl or hydrocarbyl-substituted acids or anhydrides which may be called alkyl substituted carboxylic acylating agents. The substituted carboxylic acylating agents containing halogen can then be further reacted with amines, polyamines, alcohols, amino-alcohols or metal salts to form halogen containing dispersants, esters and metal salts. It is not uncommon for the polyalkenyl-substituted carboxylic acylating agents to have chlorine contents of 0.5-1%. This corresponds to 5,000-10,000 parts per million chlorine.
Examples of U.S. patents which describe methods for preparing hydrocarbyl-substituted aliphatic carboxylic acylating agents, and particularly polyalkenyl-substituted carboxylic acylating agents utilizing various amounts of chlorine include U.S. Pat. Nos. 3,215,707 (Rense); 3,231,587 (Rense); 3,454,607 (LeSuer); 3,912,764; 4,110,349; 4,234,435 (Meinhardt); and 5,041,622 (LeSuer). These patents are incorporated herein by reference in their entirety for disclosure related to the instant invention. U.S. Pat. No. 4,234,435 describes carboxylic derivative compositions produced by reacting at least one substituted succinic acylating agent with a reactant such as amines, alcohols, reactive metals or combinations thereof. The substituted succinic acylating agent consists of polyalkenyl substituent groups and succinic groups. The substituent groups are derived from a polyalkene having an M.sub.n value of about 1300 to about 5,000 and an M.sub.w /M.sub.n value of about 1.5 to about 4. The acylating agents are characterized by the presence within their structure of an average of more than one succinic group for each equivalent weight of substituent groups. Because of the presence of the excess of succinic groups in the acylating agents, such compounds have been referred to in the art as "over succinated," and the products described in the `435 patent have also been characterized as detergents and viscosity improving additives in lubricating oil compositions. When such derivatives are incorporated into lubricating compositions, they impart sufficient fluidity modifying properties to the lubricant which are sufficient to permit elimination of all or a significant amount of viscosity index improver from multi-grade lubricant compositions containing the same.
The acylating agents utilized in preparing the lubricant additives described in U.S. Pat. No. 4,234,435 are prepared by reaction of polyisobutylene polymer with an .alpha.-.beta. unsaturated dicarboxylic acid or anhydride such as maleic anhydride in the presence of chlorine. In such instances, the products which are obtained from the reaction and the products obtained from subsequent reaction with amines, alcohols, alcohols and metal compounds contain various amounts of halogen. Due to environmental concerns, it has now become desirable to eliminate or reduce the level of chlorine. One potential solution to eliminating the chlorine contained in such lubricant and fuel additives is simply to not use chlorine in the manufacturing process. Another potential solution is to develop procedures for treating such compositions to remove the chlorine which is present. One procedure for treating various chlorine-containing organic compounds to reduce the level of chlorine therein has been described in a European patent application published under Publication No. 655,242. The procedure described therein for reducing the chlorine content of organochlorine compounds comprises introducing a source of iodine or bromine into the organochlorine compound and contacting the components of the resulting mixture for a sufficient amount of time to reduce the chlorine content without substantially incorporating iodine or bromine into the organochlorine compound. This procedure is successful in reducing the chlorine content of organochlorine compounds, but in some instances, it is desirable to even further reduce the amount of chlorine in additive compositions which are to be utilized in lubricants and fuels.
Another published method of reducing the chlorine content of organo-chlorine compounds is described in U.S. Pat. No. 5,489,390. The method comprises treating the chlorine-containing compound with an acid.
As mentioned above, one technique for reducing the amount of chlorine in additive compositions based on polyalkenyl-substituted carboxylic acylating agents is to prepare such hydrocarbon-substituted dicarboxylic acids in the absence of chlorine, and procedures have been described for preparing such compounds by the "thermal" process in which the polyolefin and the unsaturated dicarboxylic acid are heated together, optionally in the presence of a catalyst. However, when this procedure is used, it is more difficult to incorporate an excess of the succinic groups into the polyalkenyl-substituted succinic acylating agent, and dispersants prepared from such acylating agents do not exhibit sufficient viscosity index improving characteristics.
It has been proposed in the art that ashless dispersants can be prepared with succinic to polyolefin substituent ratios in excess of 1.3:1 by the thermal process when the polyolefin contains a large amount, such as at least about 70%, of the terminal groupings having an alpha-olefinic bond and/or structures capable of isomerizing to such alpha-olefinic structures. Such structures are vinylidene end groups or groups in resonance therewith and are depicted by structures I and II of Table 1. Such procedures are described in published European Patent Application 355 895 and a polymer with high vinylidene content has been available for many years through BASF. Reactive polyisobutylenes having at least 70% of their unsaturation in a terminal position are described in U.S. Pat. Nos. 4,605,808 and 4,152,499. The process described in this patent uses a complex of boron trifluoride and alcohol as catalyst, and a contact time of at least 8 minutes.
Many chlorine-containing methods of forming hydrocarbyl-substituted acylating agents have been described. Patents describing variations on the theme of reacting chlorine with an olefin and maleic anhydride are described in the patents listed above.
One method of preparing succinic acylating agents is conveniently designated as the "two-step procedure" and is described in, for example, U.S. Pat. No. 3,219,666 (Norman et al) which is incorporated herein by reference in its entirety. It involves first chlorinating the polyalkene until there is an average of at least about one chloro group for each molecular weight of polyalkene. (For purposes of this discussion, the molecular weight of the alkene is the weight corresponding to the M.sub.n value.) Chlorination involves merely contacting the polyalkene with chlorine gas until the desired amount of chlorine is incorporated into the chlorinated polyalkene. Chlorination is generally carried out at temperatures of about 75.degree. C. to about 125.degree. C. If a diluent is used in the chlorination procedure, it should be one which is not itself readily subject to further chlorination. Poly- and perchlorinated and/or fluorinated alkyl benzenes are examples of suitable diluents.
The second step in the two-step chlorination procedure is to react the chlorinated polyalkene with the maleic reactant at a temperature usually within the range of about 100.degree. C. to about 200.degree. C. The mole ratio of chlorinated polyalkene to maleic reactant is usually about 1:1.
Another procedure for preparing substituted succinic acid acylating agents utilized a process described in U.S. Pat. No. 3,912,764 (Palmer et al) which is expressly incorporate hereby by reference in its entirety.
The polyalkene and the maleic reactant are first reacted by heating them together in a "direct alkylation" procedure. When the direct alkylation step is completed, chlorine is introduced into the reaction mixture to promote reaction of the remaining maleic reactants. According to the patent, 0.3 to 2 or more moles of maleic anhydride are used in the reaction for each mole of olefin polymer; i.e., polyalkene. The direct alkylation step is conducted at temperatures of 180.degree. C. to 250.degree. C. During the chlorine-introducing stage, a temperature of 160.degree. C. to 225.degree. C. is employed. In utilizing this process to prepare the substituted succinic acylating agents useful herein, it would be necessary to use sufficient maleic reactant and chlorine to incorporate at least 1.3 succinic groups into the final product for each equivalent weight of groups derived from the polyalkene.
A further method of preparing a succinic acylating agent is disclosed in U.S. Pat. No. 3,231,587 (Rense) which is herein incorporated specifically by reference. This process, known as the "one step" process, and comprises preparing a mixture of an olefin polymer and maleic anhydride, and contacting said mixture at a temperature above about 140.degree. C. with at least about one mole of chlorine for each mole of maleic anhydride. The product of the above process, as indicated before, is a polyalkenyl-substituted succinic anhydride. The mechanism by which the product is formed is not known. It is known, however, that the process is different from one in which the olefin polymer is first chlorinated and the chlorinated polymer is then allowed to react with maleic anhydride under similar reaction conditions. The two-step process requires a considerably lengthier reaction time and results in products which are much darker in color. Also, if the olefin polymer is to be chlorinated first, the chlorination temperature should not be allowed to exceed 120.degree. C. Higher temperatures are known to cause dechlorination and thus result in products having little or no chlorine.
To carry out the process, it is preferred that the chlorine be introduced into the reaction zone after the olefin polymer has been thoroughly mixed with maleic anhydride. If the chlorine is allowed to come in contact with the olefin polymer prior to the introduction of maleic anhydride, chlorination of the polymer will take place and the advantageous results will not be obtained. The rate of introduction of the chlorine is not critical. Ordinarily, for maximum utilization of the chlorine used, the rate should be about the same as the rate of consumption of chlorine in this reaction.
The minimum temperature at which the reaction of the above process takes place at a reasonable rate is about 100.degree. C.; hence, the minimum temperature at which the process should be carried out is in the neighborhood of about 90.degree. C.-140.degree. C. The preferred temperatures usually range between about 160.degree. C. and about 220.degree. C. Higher temperatures such as 250.degree. C. or even higher may be used but usually with little advantage. The upper limit of the usable temperature is determined primarily by the decomposition point of the components in the reaction mixture.
The stoichiometry of the reaction involved in this process requires approximately equimolar amounts of the maleic anhydride and the chlorine used. For practical considerations, however, a slight excess, usually in the neighborhood of 20-30%, of chlorine is preferred in order to offset any accidental loss of this gaseous reactant from the reaction mixture. Still greater amounts of chlorine may be used but they do not appear to produce any noticeable benefits.
The relative amounts of the olefin polymer and maleic anhydride will vary according to the proportion of the succinic anhydride radicals desired in the product. Thus, for each mole of the polymer employed, one or more moles of maleic anhydride may be used depending upon whether one or more succinic anhydride radicals are to be incorporated in each polymer molecule. In general, the higher the molecular weight of the polymer, the greater the proportion of maleic anhydride which may be used. On the other hand, when a molar excess of the polymer reactant is used, the excess polymer will simply remain in the product as a diluent without any adverse effect.
Other procedures for preparing the polyalkenyl-substituted succinic acylating agents also are described in the art and may be used to prepare the carboxylic acylating compositions. For example, U.S. Pat. No. 4,110,439 (Cohen) describes another version of the two-step process, and U.S. Pat. No. 5,041,622 (LeSuer) describes a three-step process. Both of these patents are herein incorporated by references.